/*-------------------------------------------------------------------------
 *
 * spin.h
 *       Hardware-independent implementation of spinlocks.
 *
 *
 *    The hardware-independent interface to spinlocks is defined by the
 *    typedef "slock_t" and these macros:
 *
 *    void SpinLockInit(volatile slock_t *lock)
 *        Initialize a spinlock (to the unlocked state).
 *
 *    void SpinLockAcquire(volatile slock_t *lock)
 *        Acquire a spinlock, waiting if necessary.
 *        Time out and abort() if unable to acquire the lock in a
 *        "reasonable" amount of time --- typically ~ 1 minute.
 *
 *    void SpinLockRelease(volatile slock_t *lock)
 *        Unlock a previously acquired lock.
 *
 *    bool SpinLockFree(slock_t *lock)
 *        Tests if the lock is free. Returns TRUE if free, FALSE if locked.
 *        This does *not* change the state of the lock.
 *
 *    Callers must beware that the macro argument may be evaluated multiple
 *    times!
 *
 *    Load and store operations in calling code are guaranteed not to be
 *    reordered with respect to these operations, because they include a
 *    compiler barrier.  (Before PostgreSQL 9.5, callers needed to use a
 *    volatile qualifier to access data protected by spinlocks.)
 *
 *    Keep in mind the coding rule that spinlocks must not be held for more
 *    than a few instructions.  In particular, we assume it is not possible
 *    for a CHECK_FOR_INTERRUPTS() to occur while holding a spinlock, and so
 *    it is not necessary to do HOLD/RESUME_INTERRUPTS() in these macros.
 *
 *    These macros are implemented in terms of hardware-dependent macros
 *    supplied by s_lock.h.  There is not currently any extra functionality
 *    added by this header, but there has been in the past and may someday
 *    be again.
 *
 *
 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/storage/spin.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef SPIN_H
#define SPIN_H

#include "storage/s_lock.h"
#ifndef HAVE_SPINLOCKS
#include "storage/pg_sema.h"
#endif


#define SpinLockInit(lock)    S_INIT_LOCK(lock)

#define SpinLockAcquire(lock) S_LOCK(lock)

#define SpinLockRelease(lock) S_UNLOCK(lock)

#define SpinLockFree(lock)    S_LOCK_FREE(lock)


extern int    SpinlockSemas(void);
extern Size SpinlockSemaSize(void);

#ifndef HAVE_SPINLOCKS
extern void SpinlockSemaInit(void);
extern PGSemaphore *SpinlockSemaArray;
#endif

#endif                            /* SPIN_H */
